The Capstan That Went Soft
Cameron used quite a few practical effects for a film this scale, and made sure most of the close up shots would hold up well in the future (as opposed to CGI that becomes outdated). But if you look closely, it caused some very noticeable issues. For example, they used props to simulate a capstan – a revolving cylinder used to wind ropes.
At one point, a passenger is hit by one of these massive things when he falls to the bottom of the deck. Obviously, it couldn’t be made out of metal, so it was made out of foam. But that also meant that we could see the thin wrinkle once it was hit.